In recent years illumination systems are undergoing significant changes with the introduction of solid state illumination (SSL) technology that is based on using light-emitting semiconductor devices better known as LEDs (Light Emitter Diodes).
These new lamps introduce several advantages such as longer duration and lower consumption or the capacity to generate different colors in a simple manner. Furthermore, greater electricity-light conversion efficiencies and more devices with higher light outputs are attained with increasing frequency, so they are bound to replace current, conventional lamps (incandescent lamps, fluorescent lamps).
On the other hand, since it relates to a light generation process that is very different from the earlier processes, it is necessary to introduce or develop specific methods to provide these lamps with functionalities similar to those offered by conventional lamps to which users have grown accustomed. This is the case, for example, of the capacity of varying the intensity of light emitted by one and the same lamp, i.e., without using several lamps more or less of which are switched ON according to the need. In the case of SSL lamps, this light intensity control must act on the LED device.
The level of light intensity in a LED depends on the intensity of the current circulating through it, although the latter is not an efficient method to perform said control. A simpler system is based on the property of integration by the human eye which is incapable of distinguishing very rapid changes in the captured images. In the case of illumination, rapid variations in the level thereof are captured as an average intensity, therefore it is possible to change the intensity of the light captured by the human sight by introducing rapid changes between the ON and OFF states of the LED lamps and changes in the ratio between those ON and OFF periods.
Therefore, if a period of variation which is rapid enough for the human eye is established and changes are generated in the duty cycle (ON and OFF time ratio) of the LED excitation signal, it is possible to perform illumination control over such SSL lamps. This technique is also known as PWM (Pulse-Width Modulation). In the case of LED lamps for illumination, a signal frequency of more than 50 HZ is required so that the light does not flicker.
On the other hand, one of the critical lamp design parameters is related to the dissipation of the generated heat and the temperature attained by the electronic devices that may cause said devices to stop working temporarily or permanently. To that end, heat sinks and conducting elements facilitating the evacuation of this generated heat are introduced.
The temperature inside a LED Tja depends on different variables:                The electrical power consumed PLED=ILED(t)*VLED(t),        The thermal resistance between the attachment of the LED diode and the environment conditioning the temperature because it limits heat evacuation Rθja (with typical values between 325 and 650° C./W),        The room temperature Ta.        
The expression determining same is as follows:Tja=(Rθja·PLED)+Ta=(Rθja·ILED(t)·VLED(t))+Ta 
When the LED is OFF, the temperature inside the LED follows the same expression, except that now the power of the LED has the opposite sign (heat is not generated but lost), so the temperature decreases. This heat variation depends on the material and the elapsed time. The expression of the temperature attained when the LED is OFF Tjaoff is as follows:
            T      jaoff        =                  T        jaf            -              (                              R                          θ              ⁢                                                          ⁢              ja                                ·                      P            LEDoff                          )            +              T        a                        P      LEDoff        =                  dQ        ⁡                  (          t          )                    dt      where Tjaf is the temperature attained when the LED is ON and Q(t) is the function determining the value of the heat energy in the LED.
Generally, the design of the dissipation systems takes into account these equations only when the LED is ON for calculating the maximum electrical power and dissipation necessary to prevent reaching the critical temperatures that destroy the component or drastically reduce its performances. However, for PWM coding and the proposal of this invention, the formulas for LED which is OFF are also relevant, since there are periods of the signal in which excitation does not occur. In that case, the temporal temperature variation of the LED Tja can be expressed as follows.
      T    ja    =            T      a        +                  ∑        i            ⁢              (                              R                          θ              ⁢                                                          ⁢              ja                                ·                      P            LEDi                          )            where PLEDi correspond to periods in which the LED is ON or OFF.
According to the foregoing, the state of the art does not disclose an illumination control method or system for LED lamps that are capable of prolonging the service life of the lamps by reducing the attained maximum temperatures and that allow selecting the intensity of light emitted by said lamps at the same time.